In co-culture of dorsal root ganglion (DRG) and dorsal horn (DH) neurons we studied the long-term depression (LTD) caused by 5 sec(-1) low-frequency stimulation (LFS) of DRG neurons. Dual whole-cell patch clamp recording in the pairs of DRG and DH neurons was used. The monosynaptic AMPA-receptor mediated eEPSC initiated in DH neurons by LFS of DRG neurons were analyzed. LFS with durations from 60 to 360 sec affected the LTD magnitude and involved the different LTD expression mechanisms. The amplitude and variability of miniature EPSC were not changed during LTD. LFS during 60 sec did not alter the eEPSC amplitudes, but significantly increased the coefficient of variation (CV; 56.8% +/- 11.5%, n = 5; P < 0.002) and the paired-pulse ratio (PPR; 37.8% +/- 11.4%, n = 5; P < 0.05), and decreased the release probability (p; 21.9% +/- 5.6%, n = 5; P < 0.05) calculated using binomial analysis. LFS for 120 sec led to LTD (eEPSC decreased to 14% +/- 3.3%, n = 13; P < 0.005); no changes in CV, PPR and p were found. LFS for 160, 200, 240 and 360 sec induced robust LTD: eEPSC decreased to 37.3 +/- 4.3 (n = 9); 48.1 +/- 3.5 (n = 7); 58.3 +/- 2.5 (n = 8) and 57.3% +/- 2.8% (n = 8), respectively; P < 0.001. LTD induced by such LFS durations was not accompanied by significant changing in PPR and p, but showed an increase in CV: 24.4 +/- 8.6 (n = 6); 35.1 +/- 11.2 (n = 6); 37.7 +/- 12.8 (n = 7), and 38.1% +/- 9.3% (n = 8), respectively. LTD magnitude was correlated with the enhancement in CV value at different LFS duration (r = 0.96). Our data suggest that the different mechanisms could be involved in LTD expression according to duration of LFS. Thus, 60 sec LFS induces presynaptic changes, but no change in eEPSC, whereas LTD elicited by 120 and 160 sec LFS affected the postsynaptic site. LTD initiated by longer LFS (200 - 360 sec) probably was caused by a silencing of functional synapses without changes in glutamate release probability.